A number of liver function tests (LFTs) are available to test the proper function of the liver. These test for the presence of enzymes in blood that are normally most abundant in liver tissue, metabolites or products. serum proteins, serum albumin, serum globulin,

alanine transaminase, aspartate transaminase, prothrombin time, partial thromboplastin time.

Imaging tests such as transient elastography, ultrasound and magnetic resonance imaging can be used to examine the liver tissue and the bile ducts. Liver biopsy can be performed to examine liver tissue to distinguish between various conditions; tests such as elastography may reduce the need for biopsy in some situations.

Anti-viral medications are available to treat infections such as hepatitis B. Other conditions may be managed by slowing down disease progression, for example:

- By using steroid-based drugs in autoimmune hepatitis.

- Regularly removing a quantity of blood from a vein (venesection) in the iron overload condition, hemochromatosis.

- Wilson’s disease, a condition where copper builds up in the body, can be managed with drugs which bind copper allowing it to be passed from your body in urine.

- In cholestatic liver disease, (where the flow of bile is affected due to cystic fibrosis) a medication called ursodeoxycholic acid (URSO, also referred to as UDCA) may be given.

On microscopic examination of liver biopsy specimens, PBC is characterized by interlobular bile duct destruction. These histopathologic findings in primary biliary cholangitis include the following:

- Inflammation of the bile ducts, characterized by intraepithelial lymphocytes, and

- Periductal epithelioid granulomata.

To diagnose PBC, it needs to be distinguished from other conditions with similar symptoms, such as autoimmune hepatitis or primary sclerosing cholangitis (PSC).

- Abnormalities in liver enzyme tests are usually present and elevated gamma-glutamyl transferase and alkaline phosphatase (ALP) are found in early disease. Elevations in bilirubin occur in advanced disease.

- Antimitochondrial antibodies are the characteristic serological marker for PBC, being found in 90%-95% of patients and only 1% of controls. PBC patients have AMA against pyruvate dehydrogenase complex (PDC-E2), an enzyme complex that is found in the mitochondria. Those people who are AMA negative but with disease similar to PBC have been found to have AMAs when more sensitive detection methods are employed.

- Other auto-antibodies may be present:

- Abdominal ultrasound, MR scanning (MRCP) or a CT scan is usually performed to rule out blockage to the bile ducts. This may be needed if a condition causing secondary biliary cirrhosis, such as other biliary duct disease or gallstones, needs to be excluded. A liver biopsy may help, and if uncertainty remains as in some patients, an endoscopic retrograde cholangiopancreatography (ERCP), an endoscopic investigation of the bile duct, may be performed.

Most patients can be diagnosed without invasive investigation, as the combination of anti-mitochondrial antibodies and typical (cholestatic) liver enzyme tests are considered diagnostic. However, a liver biopsy is needed to determine the stage of disease.

Common findings are elevated liver enzymes and a liver ultrasound showing steatosis. An ultrasound may also be used to exclude gallstone problems (cholelithiasis). A liver biopsy (tissue examination) is the only test widely accepted as definitively distinguishing NASH from other forms of liver disease and can be used to assess the severity of the inflammation and resultant fibrosis.

Non-invasive diagnostic tests have been developed, such as FibroTest, that estimates liver fibrosis, and SteatoTest, that estimates steatosis, however their use has not been widely adopted. Apoptosis has been indicated as a potential mechanism of hepatocyte injury as caspase-cleaved cytokeratin 18 (M30-Apoptosense ELISA) in serum/plasma is often elevated in patients with NASH and tests based on these parameters have been developed; however, as the role of oncotic necrosis has yet to be examined it is unknown to what degree apoptosis acts as the predominant form of injury.

Other diagnostic tests are available. Relevant blood tests include erythrocyte sedimentation rate, glucose, albumin, and kidney function. Because the liver is important for making proteins used in coagulation some coagulation related studies are often carried out especially the INR (international normalized ratio). In people with fatty liver with associated inflammatory injury (steatohepatitis) blood tests are usually used to rule out viral hepatitis (hepatitis A, B, C and herpes viruses like EBV or CMV), rubella, and autoimmune related diseases. Hypothyroidism is more prevalent in NASH patients which would be detected by determining the TSH.

It has been suggested that in cases involving overweight patients whose blood tests do not improve on losing weight and exercising that a further search of other underlying causes is undertaken. This would also apply to those with fatty liver who are very young or not overweight or insulin-resistant. In addition those whose physical appearance indicates the possibility of a congenital syndrome, have a family history of liver disease, have abnormalities in other organs, and those that present with moderate to advanced fibrosis or cirrhosis.

In the early stages, patients with ALD exhibits subtle and often no abnormal physical findings. It is usually not until development of advanced liver disease that stigmata of chronic liver disease become apparent. Early ALD is usually discovered during routine health examinations when liver enzyme levels are found to be elevated. These usually reflect alcoholic hepatic steatosis. Microvesicular and macrovesicular steatosis with inflammation are seen in liver biopsy specimens. These histologic features of ALD are indistinguishable from those of nonalcoholic fatty liver disease. Steatosis usually resolves after discontinuation of alcohol use. Continuation of alcohol use will result in a higher risk of progression of liver disease and cirrhosis. In patients with acute alcoholic hepatitis, clinical manifestations include fever, jaundice, hepatomegaly, and possible hepatic decompensation with hepatic encephalopathy, variceal bleeding, and ascites accumulation.Tender hepatomegaly may be present, but abdominal pain is unusual. Occasionally, the patient may be asymptomatic.

In people with alcoholic hepatitis, the serum aspartate aminotransferase (AST) to alanine aminotransferase (ALT) ratio is greater than 2:1.AST and ALT levels are almost always less than 500. The elevated AST to ALT ratio is due to deficiency of pyridoxal-6-phosphate, which is required in the ALT enzyme synthetic pathway. Furthermore, alcohol metabolite–induced injury of hepatic mitochondria results in AST isoenzyme release. Other laboratory findings include red blood cell macrocytosis (mean corpuscular volume > 100) and elevations of serum γ-glutamyl transferase, alkaline phosphatase, and bilirubin levels. Folate level is reduced in alcoholic patients due to decreased intestinal absorption, increased bone marrow requirement for folate in the presence of alcohol, and increased urinary loss.The magnitude of leukocytosis reflects severity of liver injury. Histologic features include Mallory bodies, giant mitochondria, hepatocyte necrosis, and neutrophil infiltration at the perivenular area. Mallory bodies, which are also present in other liver diseases, are condensations of cytokeratin components in the hepatocyte cytoplasm and do not contribute to liver injury.Up to 70% of patients with moderate to severe alcoholic hepatitis already have cirrhosis identifiable on biopsy examination at the time of diagnosis.

Modern imaging techniques allow the diagnosis to be made more easily and without invasive imaging of the biliary tree. Commonly, the disease is limited to the left lobe of the liver. Images taken by CT scan, X-ray, or MRI show enlarged intrahepatic (in the liver) bile ducts due to ectasia. Using an ultrasound, tubular dilation of the bile ducts can be seen. On a CT scan, Caroli disease can be observed by noting the many fluid-filled, tubular structures extending to the liver. A high-contrast CT must be used to distinguish the difference between stones and widened ducts. Bowel gas and digestive habits make it difficult to obtain a clear sonogram, so a CT scan is a good substitution. When the intrahepatic bile duct wall has protrusions, it is clearly seen as central dots or a linear streak. Caroli disease is commonly diagnosed after this “central dot sign” is detected on a CT scan or ultrasound. However, cholangiography is the best, and final, approach to show the enlarged bile ducts as a result of Caroli disease.

Many drug candidates are in advanced clinical studies as : elafibranor, obeticholic acid.

PSC is generally diagnosed on the basis of having at least two of three clinical criteria after secondary causes of sclerosing cholangitis have been ruled out:

- serum alkaline phosphatase (ALP) > 1.5x the upper limit of normal for longer than 6 months;

- cholangiography demonstrating biliary strictures or irregularity consistent with PSC; and,

- liver biopsy consistent with PSC (if available).

Historically, a cholangiogram would be obtained via endoscopic retrograde cholangiopancreatography (ERCP), which typically reveals "beading" (alternating strictures and dilation) of the bile ducts inside and/or outside the liver. Currently, the preferred option for diagnostic cholangiography, given its non-invasive yet highly accurate nature, is magnetic resonance cholangiopancreatography (MRCP), a magnetic resonance imaging technique. MRCP has unique strengths, including high spatial resolution, and can even be used to visualize the biliary tract of small animal models of PSC.

Most people with PSC have evidence of autoantibodies and abnormal immunoglobulin levels. For example, approximately 80% of people with PSC have perinuclear anti-neutrophil cytoplasmic antibodies; however, this and other immunoglobulin findings are not specific to those with PSC and are of unclear clinical significance/consequence. Antinuclear antibodies and anti-smooth muscle antibody are found in 20%-50% of PSC patients and, likewise, are not specific for the disease but may identify a subgroup of PSC patients who also have autoimmune hepatitis (i.e. PSC-AIH overlap syndrome).

Other markers which may be measured and monitored are a complete blood count, serum liver enzymes, bilirubin levels (usually grossly elevated), kidney function, and electrolytes. Fecal fat measurement is occasionally ordered when symptoms of malabsorption (e.g., gross steatorrhea) are prominent.

The differential diagnosis can include primary biliary cholangitis (formerly referred to as primary biliary cirrhosis), drug-induced cholestasis, cholangiocarcinoma, IgG4-related disease, post-liver transplantation non-anastomotic biliary strictures, and HIV-associated cholangiopathy. Primary sclerosing cholangitis and primary biliary cholangitis are distinct entities and exhibit important differences, including the site of tissue damage within the liver, associations with inflammatory bowel disease (IBD), which includes ulcerative colitis and Crohn's disease, response to treatment, and risks of disease progression.

The purpose of screening for viral hepatitis is to identify people infected with the disease as early as possible. This allows for early treatment, which can prevent disease progression, and decreases transmission to others.

A1AT deficiency remains undiagnosed in many patients. Patients are usually labeled as having COPD without an underlying cause. It is estimated that about 1% of all COPD patients actually have an A1AT deficiency. Thus, testing should be performed for all patients with COPD, asthma with irreversible airflow obstruction, unexplained liver disease, or necrotizing panniculitis. The initial test performed is serum A1AT level. A low level of A1AT confirms the diagnosis and further assessment with A1AT protein phenotyping and A1AT genotyping should be carried out subsequently. The Alpha-1 Foundation offers free, confidential testing.

As protein electrophoresis does not completely distinguish between A1AT and other minor proteins at the alpha-1 position (agarose gel), antitrypsin can be more directly and specifically measured using a nephelometric or immunoturbidimetric method. Thus, protein electrophoresis is useful for screening and identifying individuals likely to have a deficiency. A1AT is further analyzed by isoelectric focusing (IEF) in the pH range 4.5-5.5, where the protein migrates in a gel according to its isoelectric point or charge in a pH gradient.

Normal A1AT is termed M, as it migrates toward the center of such an IEF gel. Other variants are less functional and are termed A-L and N-Z, dependent on whether they run proximal or distal to the M band. The presence of deviant bands on IEF can signify the presence of alpha-1 antitrypsin deficiency. Since the number of identified mutations has exceeded the number of letters in the alphabet, subscripts have been added to most recent discoveries in this area, as in the Pittsburgh mutation described above. As every person has two copies of the A1AT gene, a heterozygote with two different copies of the gene may have two different bands showing on electrofocusing, although a heterozygote with one null mutant that abolishes expression of the gene will only show one band. In blood test results, the IEF results are notated as, e.g., PiMM, where Pi stands for protease inhibitor and "MM" is the banding pattern of that person.

Other detection methods include use of enzyme-linked-immuno-sorbent-assays in vitro and radial immunodiffusion.

Alpha 1-antitrypsin levels in the blood depend on the genotype. Some mutant forms fail to fold properly and are, thus, targeted for destruction in the proteasome, whereas others have a tendency to polymerize, thereafter being retained in the endoplasmic reticulum. The serum levels of some of the common genotypes are:

- PiMM: 100% (normal)

- PiMS: 80% of normal serum level of A1AT

- PiSS: 60% of normal serum level of A1AT

- PiMZ: 60% of normal serum level of A1AT

- PiSZ: 40% of normal serum level of A1AT

- PiZZ: 10-15% (severe alpha-1 antitrypsin deficiency)

Diagnosis is made by an assessment of symptoms, physical exam, and medical history, in conjunction with blood tests, a liver biopsy, and imaging. Diagnosis is often made following investigation of prolonged jaundice that is resistant to phototherapy and/or exchange transfusions, with abnormalities in liver enzyme tests. Ultrasound or other forms of imaging can confirm the diagnosis. Further testing may include radioactive scans of the liver and a liver biopsy.

Diagnosis of hepatitis is made on the basis of some or all of the following: a patient's signs and symptoms, medical history including sexual and substance use history, blood tests, imaging, and liver biopsy. In general, for viral hepatitis and other acute causes of hepatitis, the patient's blood tests and clinical picture are sufficient for diagnosis. For other causes of hepatitis, especially chronic causes, blood tests may not be useful. In this case, liver biopsy is the gold standard for establishing the diagnosis as histopathologic analysis is able to reveal the precise extent and pattern of inflammation and fibrosis. However, liver biopsy is typically not the initial diagnostic test because it is invasive and is associated with a small but significant risk of bleeding that is increased in patients with liver injury and cirrhosis.

Blood testing includes liver enzymes, serology (i.e. for autoantibodies), nucleic acid testing (i.e. for hepatitis virus DNA/RNA), blood chemistry, and complete blood count. Characteristic patterns of liver enzyme abnormalities can point to certain causes or stages of hepatitis. Generally, AST and ALT are elevated in most cases of hepatitis regardless of whether the patient shows any symptoms. However, the degree of elevation (i.e. levels in the hundreds vs. in the thousands), the predominance for AST vs. ALT elevation, and the ratio between AST and ALT are informative of the diagnosis.

Ultrasound, CT, and MRI can all identify steatosis (fatty changes) of the liver tissue and nodularity of the liver surface suggestive of cirrhosis. CT and especially MRI are able to provide a higher level of detail, allowing visualization and characterize such structures as vessels and tumors within the liver. Unlike steatosis and cirrhosis, no imaging test is able to detect liver inflammation (i.e. hepatitis) or fibrosis. Liver biopsy is the only definitive diagnostic test that is able to assess inflammation and fibrosis of the liver.

The differential diagnoses are extensive and include: Alagille syndrome, alpha-1-antitrypsin deficiency, Byler disease (progressive familial intrahepatic cholestasis), Caroli disease, choledochal cyst, cholestasis, congenital cytomegalovirus disease, congenital herpes simplex virus infection, congenital rubella, congenital syphilis, congenital toxoplasmosis, cystic fibrosis, galactosemia, idiopathic neonatal hepatitis, lipid storage disorders, neonatal hemochromatosis, and total parenteral nutrition-associated cholestasis.

Cholestasis can be suspected when there is an elevation of both 5'-nucleotidase and ALP enzymes. With a few exceptions, the optimal test for cholestasis would be elevations of serum bile acid levels. However, this is not normally available in most clinical settings. The gamma-glutamyl transferase (GGT) enzyme was previously thought to be helpful in confirming a hepatic source of ALP; however, GGT elevations lack the necessary specificity to be a useful confirmatory test for ALP. Normally GGT and ALP are anchored to membranes of hepatocytes and are released in small amounts in hepatocellular damage. In cholestasis, synthesis of these enzymes is induced and they are made soluble. GGT is elevated because it leaks out from the bile duct cells due to pressure from inside bile ducts.

In a later stage of cholestasis AST, ALT and bilirubin may be elevated due to liver damage as a secondary effect of cholestasis.

The treatment depends on clinical features and the location of the biliary abnormality. When the disease is localized to one hepatic lobe, hepatectomy relieves symptoms and appears to remove the risk of malignancy. Good evidence suggests that malignancy complicates Caroli disease in roughly 7% of cases.

Antibiotics are used to treat the inflammation of the bile duct, and ursodeoxycholic acid is used for hepatolithiasis. Ursodiol is given to treat cholelithiasis. In diffuse cases of Caroli disease, treatment options include conservative or endoscopic therapy, internal biliary bypass procedures, and liver transplantation in carefully selected cases. Surgical resection has been used successfully in patients with monolobar disease. An orthotopic liver transplant is another option, used only when antibiotics have no effect, in combination with recurring cholangitis. With a liver transplant, cholangiocarcinoma is usually avoided in the long run.

Family studies are necessary to determine if Caroli disease is due to inheritable causes. Regular follow-ups, including ultrasounds and liver biopsies, are performed.

There exist other causes of excess iron accumulation, which have to be considered before haemochromatosis is diagnosed.

- African iron overload, formerly known as Bantu siderosis, was first observed among people of African descent in Southern Africa. Originally, this was blamed on ungalvanised barrels used to store home-made beer, which led to increased oxidation and increased iron levels in the beer. Further investigation has shown that only some people drinking this sort of beer get an iron overload syndrome, and that a similar syndrome occurred in people of African descent who have had no contact with this kind of beer ("e.g.," African Americans). This led investigators to the discovery of a gene polymorphism in the gene for ferroportin which predisposes some people of African descent to iron overload.

- Transfusion haemosiderosis is the accumulation of iron, mainly in the liver, in patients who receive frequent blood transfusions (such as those with thalassaemia).

- Dyserythropoeisis, also known as myelodysplastic syndrome, is a disorder in the production of red blood cells. This leads to increased iron recycling from the bone marrow and accumulation in the liver.

HCC remains associated with a high mortality rate, in part related to initial diagnosis commonly at an advanced stage of disease. As with other cancers, outcomes are significanty improved if treatment is initiated earlier in the disease process. Because the vast majority of HCC occurs in people with certain chronic liver diseases, especially those with cirrhosis, liver screening is commonly advocated in this population. Specific screening guidelines continue to evolve over time as evidence of its clinical impact becomes available. In the United States, the most commonly observed guidelines are those published by the American Association for the Study of Liver Diseases (AASLD). The AASLD recommends screening people with cirrhosis with ultrasound every 6 months, with or without measurement of blood levels of tumor marker AFP. Elevated levels of AFP are associated with active HCC disease, although inconsistently reliable. At levels >20 sensitivity is 41-65% and specificity is 80-94%. However, at levels >200 sensitivity is 31, specificity is 99%.

On US, HCC often appears as a small hypoechoic lesion with poorly defined margins and coarse irregular internal echoes. When the tumor grows, it can sometimes appear heterogeneous with fibrosis, fatty change, and calcifications. This heterogeneity can look similar to cirrhosis and the surrounding liver parenchyma. A systematic review found that the sensitivity was 60 percent (95% CI 44-76%) and specificity was 97 percent (95% CI 95-98%) compared with pathologic examination of an explanted or resected liver as the reference standard. The sensitivity increases to 79% with AFP correlation.

There remains controversy as to the most effective screening protocols. For example, while there is data to support decreased mortality related to screening in people with hepatitis B infection, the AASLD notes that “there are no randomized trials [for screening] in Western populations with cirrhosis secondary to chronic hepatitis C or fatty liver disease, and thus there is some controversy surrounding whether surveillance truly leads to a reduction in mortality in this population of patients with cirrhosis.”

Liver biopsies involve taking a sample of tissue from the liver, using a thin needle. The amount of iron in the sample is then quantified and compared to normal, and evidence of liver damage, especially cirrhosis, measured microscopically. Formerly, this was the only way to confirm a diagnosis of haemochromatosis but measures of transferrin and ferritin along with a history are considered adequate in determining the presence of the malady. Risks of biopsy include bruising, bleeding and infection. Now, when a history and measures of transferrin or ferritin point to haemochromatosis, it is debatable whether a liver biopsy is still necessary to quantify the amount of accumulated iron.

Methods of diagnosis in HCC have evolved with the improvement in medical imaging. The evaluation of both asymptomatic patients and those with symptoms of liver disease involves blood testing and imaging evaluation. Although historically a biopsy of the tumor was required to prove the diagnosis, imaging (especially MRI) findings may be conclusive enough to obviate histopathologic confirmation.

Mutation analysis of the "ATP7B" gene, as well as other genes linked to copper accumulation in the liver, may be performed. Once a mutation is confirmed, it is possible to screen family members for the disease as part of clinical genetics family counseling. Regional distributions of genes associated with Wilson's disease are important to follow, as this can help clinicians design appropriate screening strategies. Since mutations of the WD gene vary between populations, research and genetic testing done in countries like the USA or United Kingdom can pose problems as they tend to have more mixed populations.

The development of any of the cancers associated with PSC predicts a poor prognosis. Complications from PSC-associated cancers account for 40% of deaths from PSC. Primary sclerosing cholangitis is one of the major known risk factors for cholangiocarcinoma, a cancer of the biliary tree, for which the lifetime risk among patients with PSC is 10-15%. This represents a 400-fold greater risk of developing cholangiocarcinoma compared to the general population. Surveillance for cholangiocarcinoma in patients with PSC is encouraged, with some experts recommending annual surveillance with a specialized imaging study and serum markers, although consensus regarding the modality and interval has yet to be established. Similarly, a screening colonoscopy is recommended in people who receive a new diagnosis of primary sclerosing cholangitis since their risk of colorectal cancer is 10 times higher than that of the general population.

PSC is strongly associated with inflammatory bowel disease (IBD), in particular ulcerative colitis (UC) and to a lesser extent Crohn's disease. As many as 5% of patients with IBD are co-diagnosed with PSC and approximately 70% of people with PSC have IBD. Of note, the presence of colitis appears to be associated with a greater risk of liver disease progression and bile duct cancer (cholangiocarcinoma) development, although this relationship remains poorly understood. Close monitoring of PSC patients is vital.

Various forms of gallbladder disease such as gallstones and gallbladder polyps are also common in those with PSC. Approximately 25% of people with PSC have gallstones. Ultrasound surveillance of the gallbladder every year is recommended for people with PSC. Any person with PSC who is found to have a mass in the gallbladder should undergo surgical removal of the gallbladder due to the high risk of cholangiocarcinoma. Osteoporosis (hepatic osteodystrophy) and hypothyroidism are also associated with PSC.

While Gilbert's syndrome is considered harmless, it is clinically important because it may give rise to a concern about a blood or liver condition, which could be more dangerous. However, these conditions have additional indicators:

- Hemolysis can be excluded by a full blood count, haptoglobin, lactate dehydrogenase levels, and the absence of reticulocytosis (elevated reticulocytes in the blood would usually be observed in haemolytic anaemia).

- Viral hepatitis can be excluded by negative blood samples for antigens specific to the different hepatitis viruses.

- Cholestasis can be excluded by normal levels of bile acids in plasma, the absence of lactate dehydrogenase, low levels of conjugated bilirubin, and ultrasound scan of the bile ducts.

- More severe types of glucuronyl transferase disorders such as Crigler–Najjar syndrome (types I and II) are much more severe, with 0–10% UGT1A1 activity, with sufferers at risk of brain damage in infancy (type I) and teenage years (type II).

- Dubin–Johnson syndrome and Rotor syndrome are rarer autosomal recessive disorders characterized by an increase of conjugated bilirubin.

- In GS, unless another disease of the liver is also present, the liver enzymes ALT/SGPT and AST/SGOT, as well as albumin, are within normal ranges.

If a liver biopsy is needed for diagnosis of the condition, the mother should be appropriately stabilized and treated to reduce bleeding related complications. The diagnosis can be made by a frozen-section (as opposed to a specimen in formalin) that is stained with the Oil red O stain, that shows microvesicular steatosis (or small collections of fat within the liver cells). The microvesicular steatosis usually spares zone one of the liver, which is the area closest to the hepatic artery. On the regular trichrome stain, the liver cell cytoplasm shows a foamy appearance due to the prominence of fat. Necrosis is rarely seen. The diagnosis can be enhanced by electron microscopy which can be used to confirm the presence of microvesicular steatosis, and specifically the presence of megamitochondria and paracrystalline inclusions. Liver diseases with similar appearances include Reye's syndrome, drug-induced hepatitis from agents with mitochondrial toxicity, including nucleoside reverse transcriptase inhibitors used to treat HIV, and a rare condition known as Jamaican vomiting sickness which is caused by the eating of the unripened Ackee fruit.